The present invention relates to an apparatus for detecting full-closure of a throttle, which is used, for example, in an electronic control system of a car internal combustion engine to obtain a reference to be used for detection of an idling state and for calculation of throttle opening information.
In an internal combustion engine, detection of the opening of a throttle valve is necessary for calculation of the quantity of fuel injection, the timing of ignition, etc. A throttle opening detecting mechanism is used for detecting the throttle opening.
FIG. 9 shows an example of the configuration of such a throttle opening detecting mechanism for detecting the operating state of a throttle valve. This mechanism has a throttle shaft 11 directly connected to the throttle valve provided in a suction pipe. The throttle shaft 11 is mounted so as to be rotatable relative to a housing 12 and is arranged to rotate with the operation of the throttle valve. Sliders 131 and 132 are fixed to the throttle shaft 11 while keeping a predetermined relative angle. A printed resistor 14 shaped like a circular arc is provided on a surface of the housing 12 facing the slider 131. Opposite ends of the resistor 14 are connected to a constant voltage source and a ground terminal respectively, so that a voltage corresponding to the contact position of the slider 131 contacting with the resistor 14, that is, a proportionally divided voltage corresponding to the opening position of the throttle valve, is outputted as a voltage corresponding to the opening of the throttle valve.
In the throttle opening detecting mechanism thus configured, a detection output voltage is minimized when the throttle valve comes into a fully-closed state. The minimum value of the detection output voltage is stored as a throttle full-closure position so that the opening of the throttle is detected on the basis of the voltage detected by the detecting mechanism by reference to the minimum voltage value corresponding to the throttle full-closure position.
In the throttle opening detecting mechanism thus configured, however, the constituent members of this mechanism have coefficients of linear expansion which are different from each other depending on the change of temperature in the state where the housing 12 holding the resistor 14, and the like, for detecting a divisional voltage is incorporated within a body of the suction pipe. Accordingly, a delicate voltage change occurs in spite of no change of the throttle opening. Accordingly, when, for example, the temperature rises in accordance with the operation of an internal combustion engine after the minimum value of the throttle opening is stored in a low temperature state at the time of starting-up, or the like, of the internal engine, the output voltage of the throttle opening detecting mechanism is shifted, for example, toward a larger value in the above-mentioned condition in which the throttle valve is fully closed.
In such a case, accordingly, if the opening of the throttle is judged by reference to the throttle full-closure voltage in a low temperature state, the voltage detected by the throttle opening detecting mechanism has a value which is larger than the full-closure voltage in a low temperature state in spite of the fact that the throttle valve is actually set to the full-closure position, so that the throttle valve is decided not to be in a fully closed state. That is, a decision is made that the idling is off in spite of the fully closed state of the throttle valve.